With an increase in the number of semiconductor devices packed on a single printed circuit board, more importance is being placed on the issue of heat dissipation from printed circuit boards having thereon heat-generating electronic components. For a heat-dissipating mechanism, creation of a heat conductive path for connecting a high temperature region to a low temperature region has been proposed.
Various heat-dissipating sheets have been developed as products having such a heat conductive path formed therein. A heat-dissipating sheet is required to have steady levels of heat conductivity, strength, and shielding ability. Therefore, to improve heat conductivity and other properties of a heat-dissipating sheet, a composition comprising a graphite material is being considered for use in sheet form.
For example, Japanese Patent Laid-Open No. 2007-224265 proposes a heat conductive composition comprising: graphite particles having an aspect ratio in a range of 10 to 20, and an average particle size of 10 μm to 200 μm; and a matrix of thermosetting resin with the particles dispersed therein.
Generally, the heat conductivity of a composition improves with an increase in graphite particle content. However, as a graphite particle content increases, the flexibility of the composition may decrease or a sheet formed by the composition may become fragile.
If a compact formed by the composition is used for dissipating heat from electronic equipment, the compact is used between objects. If the compact has high hardness, the compact cannot absorb the surface roughness of the objects because of its low flexibility. Thus, air on the surfaces of the objects reduces a heat transfer rate.
Hence, an improvement in the heat transfer rate of the composition is limited only by dispersing graphite particles into the matrix of thermoplastic resin as described in Japanese Patent Laid-Open No. 2007-224265.
In view of the circumstances, an object of the present invention is to provide an anisotropic heat conductive composition having high heat conductivity and flexibility.